U.S. patent application number 17/355565 was filed with the patent office on 2021-10-14 for electrolysis device having a converter and method for providing instantaneous reserve power for an ac voltage grid.
The applicant listed for this patent is SMA Solar Technology AG. Invention is credited to Andreas Falk, Christian Hardt.
Application Number | 20210317588 17/355565 |
Document ID | / |
Family ID | 1000005727386 |
Filed Date | 2021-10-14 |
United States Patent
Application |
20210317588 |
Kind Code |
A1 |
Falk; Andreas ; et
al. |
October 14, 2021 |
ELECTROLYSIS DEVICE HAVING A CONVERTER AND METHOD FOR PROVIDING
INSTANTANEOUS RESERVE POWER FOR AN AC VOLTAGE GRID
Abstract
A method for operating an electrolysis device, having a
converter which is connected on an AC voltage side to an AC voltage
grid via a decoupling inductance and draws an AC active power from
the AC voltage grid, and an electrolyzer, which is connected to the
converter on the DC voltage side, is provided. The method includes
operating the electrolysis device, when a grid frequency
corresponds to a nominal frequency of the ACT voltage grid and is
substantially constant over a time period, with an electrical power
which is between 50% and 100% of a nominal power of the
electrolyzer, and operating the converter in a voltage-impressing
manner, such that an AC active power drawn from the AC voltage grid
is changed on the basis of a change and/or a rate of change of the
grid frequency in the AC voltage grid.
Inventors: |
Falk; Andreas; (Kassel,
DE) ; Hardt; Christian; (Kassel, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SMA Solar Technology AG |
Niestetal |
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DE |
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|
Family ID: |
1000005727386 |
Appl. No.: |
17/355565 |
Filed: |
June 23, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP2019/083382 |
Dec 3, 2019 |
|
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17355565 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 9/65 20210101; C25B
15/02 20130101; H02M 3/04 20130101 |
International
Class: |
C25B 15/02 20060101
C25B015/02; C25B 9/65 20060101 C25B009/65 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2018 |
DE |
10 2018 133 641.1 |
Claims
1. A method for operating an electrolysis device having a
converter, which is connected, on an AC voltage side, to an AC
voltage grid via a decoupling inductance and draws an AC active
power from the AC voltage grid, and an electrolyzer, which is
connected to the converter on a DC voltage side, comprising:
operating the electrolysis device, when a grid frequency
corresponds to a nominal frequency of the AC voltage grid and is
substantially constant over a time period, with an electrical power
which is between 50% and 100% of a nominal power of the
electrolyzer; and operating the converter in a voltage-impressing
manner, such that an AC active power drawn from the AC voltage grid
is changed on the basis of a change and/or a rate of change of the
grid frequency in the AC voltage grid.
2. The method as claimed in claim 1, wherein the converter provides
an instantaneous reserve power, wherein when operating in a
voltage-impressing manner the converter emulates a behavior of a
synchronous machine with respect to frequency changes in the AC
voltage grid or uses droop mode control which comprises a
frequency/power characteristic curve.
3. The method as claimed in claim 1, wherein the change in the AC
active power drawn from the AC voltage grid results in a change in
a DC voltage at the electrolyzer, and wherein the change in the DC
voltage at the electrolyzer results in a change in a DC power
consumed by the electrolyzer, which change corresponds to the
change in the AC active power.
4. The method as claimed in claim 1, further comprising producing a
voltage transformation between the electrolyzer and the converter
using a first DC/DC converter.
5. The method as claimed in claim 4, further comprising: exchanging
electrical power between the converter and a PV generator connected
on the DC voltage side, wherein the PV generator is connected to a
DC link circuit in parallel with the electrolyzer, and feeding an
electrical power generated by the PV generator into the
electrolyzer or into the AC voltage grid.
6. The method as claimed in claim 4, further comprising:
stabilizing the voltage of the DC link circuit using the first
DC/DC converter; and controlling the first DC/DC converter using
feedforward control to set a DC current setpoint of the first DC/DC
converter on the basis of a phase difference between a grid voltage
and an AC voltage at an input of the converter.
7. The method as claimed in claim 1, further comprising exchanging
electrical power between the converter and a battery connected on
the DC voltage side, wherein the battery is connected to a DC link
circuit in parallel with the electrolyzer via a second DC/DC
converter.
8. The method as claimed in claim 7, further comprising:
stabilizing the voltage of the DC link circuit using the second
DC/DC converter; and controlling the second DC/DC converter using
feedforward control to set a DC current setpoint value of the
second DC/DC converter on the basis of a phase difference between a
grid voltage and an AC voltage at an input of the converter.
9. An electrolysis device, comprising: an electrolyzer; and a
converter connected to the electrolyzer, wherein the converter is
configured to draw electrical AC active power from an AC voltage
grid, and wherein the converter is further configured to be
operated in a voltage-impressing manner, such that a change in a
grid frequency in the AC voltage grid causes a change in an active
power drawn from the AC voltage grid.
10. The electrolysis device as claimed in claim 9, further
comprising a first DC/DC converter disposed between the
electrolyzer and the converter.
11. The electrolysis device as claimed in claim 9, further
comprising a photovoltaic generator connected to a DC link circuit
in parallel with the electrolyzer on a DC voltage side of the
electrolysis device.
12. The electrolysis device as claimed in claim 9, further
comprising a battery connected to a DC link circuit of the
electrolysis device in parallel with the electrolyzer via a second
DC/DC converter on a DC voltage side of the electrolysis
device.
13. A method for providing instantaneous reserve power for an AC
voltage grid by means of a converter which draws electrical AC
power from the AC voltage grid and supplies an electrolyzer with
electrical DC power, wherein the converter is operated in a
voltage-impressing manner, such that a change in the grid frequency
in the AC voltage grid causes a change in the AC power drawn from
the AC voltage grid.
14. The method as claimed in claim 13, wherein, at a grid frequency
which corresponds to a nominal frequency of the AC voltage grid,
the active power drawn from the AC voltage grid and supplied to the
electrolyzer is between 50% and 100% of a nominal power of the
electrolyzer.
15. The method as claimed in claim 13, wherein the converter
exchanges electrical power with a battery connected on the DC
voltage side if a change in the grid frequency causes a change in
the AC power and the DC power supplied to the electrolyzer is at an
edge of an operating range of the electrolyzer, wherein the
operating range is limited by a lower onset power of between 10%
and 20% of the nominal power and an upper maximum power of between
80% and 100% of the nominal power of the electrolyzer, wherein the
battery is connected to a DC link circuit of the converter in
parallel with the electrolyzer via a DC/DC converter.
16. The method as claimed in claim 15, wherein the converter
exchanges electrical power with a photovoltaic generator connected
on a DC voltage side of the converter, wherein, in the case of a
grid frequency which corresponds to a nominal frequency of the AC
voltage grid, the PV generator is operated at a maximum power point
and the electrolyzer is operated with nominal power, wherein the
power of the PV generator is reduced if a change in the grid
frequency occurs which causes the converter to reduce an AC power
currently being fed in or to increase an AC power currently being
drawn, and wherein the electrical DC power of the electrolyzer is
reduced if a change in the grid frequency occurs which causes the
converter to increase an AC power currently being fed in or to
reduce an AC power currently being drawn.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International Patent
Application number PCT/EP2019/083382, filed on Dec. 3, 2019, which
claims priority to German Patent Application number 10 2018 133
641.1, filed on Dec. 27, 2018, and is hereby incorporated by
reference in its entirety.
FIELD
[0002] The disclosure relates to an electrolysis device having a
converter, to a method for operating an electrolysis device having
a converter, and to a method for providing instantaneous reserve
power for an AC voltage grid.
BACKGROUND
[0003] In an AC voltage grid which is constructed as a national
integrated grid, deviations of the grid frequency from a nominal
frequency of the AC voltage grid may arise on account of an
imbalance between electrical power which is fed in and drawn
electrical power. This imbalance and therefore the frequency
deviation can be counteracted by virtue of devices, which can feed
electrical power into the AC voltage grid and/or can draw
electrical power from the AC voltage grid, varying the power fed in
or drawn by them. In particular, at frequencies above the nominal
frequency, the power which is fed in can be reduced or the power
which is drawn can be increased, whereas, at frequencies below the
nominal frequency, the power which is fed in is increased or the
power which is drawn is reduced.
[0004] The respective change in the power in direct or indirect
response to a frequency deviation is referred to as balancing
power. In some AC voltage grids, in particular in the European
integrated grid, the provision of this balancing power is organized
in stages which build on one another in terms of time. The first
control stage, the so-called instantaneous control, is ensured by
means of devices which change their power in direct and immediate
response to a frequency change. In the second control stage, the
so-called primary control, which comes into effect in the event of
a sustained frequency deviation, use is made of devices which
specifically adjust their power on the basis of a characteristic
curve as a function of the deviation of the grid frequency from the
nominal frequency. In the third stage, the so-called secondary
control, a likely persistent or foreseeable power imbalance in the
AC voltage grid is counteracted in a planned manner by virtue of
devices being instructed by a superordinate control device to
suitably change their electrical power.
[0005] The prior art discloses devices which exchange electrical
power between the AC voltage grid and a DC unit operating with
direct current. The DC unit may comprise an energy generator, for
example a photovoltaic generator, the power of which is converted
in an inverter and is fed into the AC voltage grid.
DE102005046919A1 discloses a method for buffering electrical wind
energy generated from wind power by means of an electrolysis
device, such that the wind power plant can provide balancing power.
EP2705175A1 discloses an energy management system comprising an
electrolysis system which can be used to provide balancing
power.
[0006] The converters of such devices generally operate in this
case in a current-impressing manner by virtue of a setpoint for the
DC power being converted into a corresponding setpoint for the AC
current and this AC current being fed into the AC voltage grid. The
DC unit may also comprise a DC load, for example a non-reactive
resistor, a machine or an electrochemical installation, operated by
means of a current-impressing converter which draws AC power from
the AC voltage grid and makes it available to the DC load as DC
power. A setpoint for the DC power is likewise predefined for this
current-impressing converter and is transformed, in a controller,
into a setpoint for an AC current to be drawn from the AC voltage
grid, such that the AC power is a function of the DC power.
[0007] Such converters may be, in particular, in the form of
thyristor rectifiers or self-commutated IGBT converters which are
synchronized with the AC voltage grid on the basis of a frequency
measurement. In the event of a frequency change, this frequency
measurement must first of all adjust to the new frequency before
the setpoint for the DC power and consequently the AC power are
adapted to the new situation. In this respect, a current-impressing
converter cannot immediately respond to a frequency change in the
AC voltage grid. On account of this delayed response, DC loads
which are connected to the AC voltage grid via a converter operated
in such a conventionally current-impressing manner are not suitable
for providing instantaneous balancing power or instantaneous
reserve.
[0008] DE102016115182A1 discloses a method for providing
instantaneous reserve in an AC voltage grid, in which the power of
a current-impressing converter is adjusted to an instantaneous
reserve setpoint by means of a current controller. The setpoint is
generated from a phase error signal from a PLL control loop which
uses the AC voltages of the AC voltage grid as input variables. A
current-impressing converter proves to be advantageous here over a
voltage-impressing converter, in particular in the case of
photovoltaic generators as energy sources.
[0009] EP2182626A1 discloses a method for operating a power
converter, in which semiconductor switches are controlled
selectively or in combination by means of voltage-impressing and/or
current-impressing modulation. As a result, the intention is to
advantageously combine the properties of the different types of
modulation, which produce a voltage-impressing or
current-impressing behavior of the power converter, which are
described in detail in EP2182626A1.
[0010] Devices which are used during the first of the control
stages mentioned at the outset for instantaneous control comprise,
in particular, so-called synchronous generators which feed power
into the grid or synchronous machines which draw power from the
grid. Such synchronous generators and synchronous machines
generally comprise rotating masses which have an inherent inertia.
Synchronous machines and synchronous generators contribute to
stabilizing the grid frequency by way of their electrical behavior,
which is well known to a person skilled in the art, by virtue of
their electrical power depending on the phase difference between
the AC voltage of the AC voltage grid and the rotational frequency
of the rotating mass on account of the inherent inertia. In other
words, by virtue of its inertial flywheel mass, a synchronous
generator or a synchronous machine can immediately respond to
frequency changes and can also immediately counteract them.
[0011] In this case, it is assumed, according to the prior art,
that the behavior of a synchronous generator can be emulated only
with a device on the DC voltage side which is directly connected to
the grid via a voltage-impressing converter. Such a converter, in
which the switching commands for power semiconductor switches are
derived from an AC setpoint for the input-side AC voltage of the
converter, responds to a grid frequency change immediately, that is
to say without control delays. Therefore, the device on the DC
voltage side must also be able to immediately consume or emit
energy and, for this purpose, must be directly connected to a DC
link of the converter. Such a device on the DC voltage side
comprises, for example, a battery which is connected to the grid
via a voltage-setting converter and can immediately consume or emit
energy. In this case, the voltage-impressing control would be
greatly hindered by a control delay of any DC/DC converter for
adapting the DC voltage or would even become impossible. This also
applies, in particular, to a single-stage converter which has
connected to it a photovoltaic generator which is operated with a
PV voltage close to the grid rectification voltage, with the result
that even small DC voltage dips can result in considerable
distortions of the alternating current fed in by the converter;
such dips must be prevented by means of suitable control of the DC
source.
[0012] DE102010030093A1 discloses a device and a method for
controlling the exchange of electrical energy between an AC voltage
grid and an installation connected to the AC voltage grid, wherein
the installation can include a consumer, a generator and/or an
energy store. The device comprises a converter, in which the power
exchanged with the AC voltage grid can be adjusted on the basis of
active power/frequency statics. The converter additionally has a
so-called synchronous machine emulator, by means of which the
converter models the dynamic behavior of a synchronous machine. As
a result, grid frequency support, in particular, is intended to be
carried out in the transient and/or sub-transient time range,
wherein the response of the device to a grid frequency change can
be carried out in a differential manner, that is to say the change
in the power is greater, the higher the temporal rate of change of
the grid frequency. In this case, non-reactive resistors or
machines are used as consumers, possibly in combination with a
storage device for thermal, mechanical or chemical energy. As a
result, some of the capacity of the consumers or some of the energy
which is or can be stored in an energy store is available for grid
support.
[0013] Further embodiments of synchronous machine emulation are
known, for example, from DE102006047792A1, in which a so-called
virtual synchronous machine (VISMA) is used for grid support,
wherein the behavior of a synchronous machine is approximated by
continuously solving differential equations, and from EP3376627A1
which describes a voltage-impressing converter (Voltage Source
Inverter, VSI), the control system of which comprises a structure
for generating a virtual inertia, with the result that the
converter emulates the behavior of a synchronous generator.
[0014] EP1286444B1 discloses so-called droop mode control for an
inverter, wherein the inverter is operated on the basis of
frequency statics f(P) and voltage statics U(Q), with the result
that the inverter immediately responds to frequency changes in the
AC voltage grid with a change in the active power and, in this
respect, is suitable for parallel operation with further inverters
and, in particular, for setting up an island grid.
[0015] U.S. Pat. No. 7645931 discloses a device having a converter
connected to an AC voltage grid, a photovoltaic generator and an
electrolyzer, wherein the electrolyzer is permanently operated at
an optimum operating point with a corresponding power, wherein the
electrical power for operating the electrolyzer is guided to the
electrolyzer either from the PV generator via a DC/DC converter or
from the AC voltage grid via the converter.
[0016] EP2894722B1 discloses an arrangement for supplying an
electrolyzer with direct current, in which semiconductor components
of a rectifier, in particular its thyristors, are divided into two
groups, wherein one of the groups is each directly arranged at one
of the two DC connections of the electrolyzer. The rectifier may be
connected to a medium-voltage grid via at least one transformer,
and the output power of the rectifier can be set in a range between
20% and 50% of the maximum output power of the rectifier by
controlling the thyristors.
SUMMARY
[0017] The disclosure is directed to a method for operating an
electrolysis device connected to an AC voltage grid and an
electrolysis device, with which an electrolyzer can be operated and
instantaneous reserve power for stabilizing the grid frequency of
the AC voltage grid can be provided at the same time.
[0018] In a method for operating an electrolysis device having a
converter, which is connected, on the AC voltage side, to an AC
voltage grid via a decoupling inductance and draws an AC active
power from the AC voltage grid, and an electrolyzer, which is
connected to the converter on the DC voltage side and, in the case
of a grid frequency which corresponds to a nominal frequency of the
AC voltage grid and is constant over time, is operated with an
electrical power which is between 50% and 100% of a nominal power
of the electrolyzer, wherein the converter is operated in a
voltage-impressing manner, such that the AC active power drawn from
the AC voltage grid is immediately changed on the basis of a change
and/or a rate of change of the grid frequency in the AC voltage
grid.
[0019] In comparison with conventional methods for operating an
electrolysis device, the method according to the disclosure is
distinguished, in particular, by the fact that the converter is
operated in a voltage-impressing manner. This means, for example,
that a setpoint for the input-side AC voltage of the converter is
predefined when controlling the converter and the converter behaves
such that this desired voltage is achieved if possible, in
particular irrespective of the current which is then flowing. In
addition, voltage-impressing operation of the converter involves
the AC current drawn from the AC voltage grid depending on the grid
frequency in such a manner that a change in the grid frequency
results in an immediate change in the power drawn from the AC
voltage grid, in particular irrespective of which sink is connected
to that end of the converter which is opposite the AC voltage grid.
In this case, the change in the power may be proportional to a rate
of change of the grid frequency, in particular.
[0020] Precisely this immediate change in the power on the basis of
a change in the grid frequency also belongs to the inherent
behavior of a synchronous machine. In contrast to this,
current-impressing operation has an inherent delay by virtue of a
setpoint for the AC current being predefined, wherein this setpoint
can be adapted at best indirectly in the case of frequency changes
in order to stabilize the frequency, for example using a P(f)
characteristic curve.
[0021] The immediate responses to changes in the grid frequency,
associated with voltage-impressing operation, in the form of
changes in the AC active power drawn from the AC voltage grid can
be immediately passed on to an electrolyzer even though the
electrolyzer itself is not able to make an accordingly fast change
in the converted power. Nevertheless, a change in the AC active
power can be immediately passed on to the electrolyzer via the
converter, for example by means of a corresponding change in the DC
voltage applied by the converter to the electrolyzer. The change in
the DC voltage results, via a voltage/current characteristic curve
of the electrolyzer, in a change in the power consumed by the
electrolyzer. In this case, the electrolyzer is operated according
to the disclosure before the change, that is to say in the case of
a constant grid frequency, at between 50% and 100% of its nominal
power, wherein the nominal power of the electrolyzer is below a
maximum power of the electrolyzer and can correspond, in
particular, to the power at the maximum efficiency of the
electrolyzer.
[0022] The DC power of the electrolyzer can therefore be reduced or
increased, which results in a change in the substance conversion in
the electrolyzer. In this case, on account of its structure, an
electrolyzer can permanently process the additional or reduced
conversion occurring briefly as a result of a change in the DC
power only when further measures for operating the electrolyzer
take place, for example a change in the output of pumps for
circulating electrolyte or for removing gases which are produced.
However, these further measures have a comparatively high inertia,
with the result that it is possible to stabilize the operation of
the electrolyzer after a sudden change in the applied voltage only
with a delay.
[0023] On the other hand, the voltage-impressing operation of the
converter is distinguished by the fact that the change in the
active power drawn from the AC voltage grid depends substantially
on the change and/or the rate of change of the grid frequency, with
the result that the active power returns to an initial value as
soon as there is no longer a change in the grid frequency, that is
to say, in particular, if the rate of change is equal to zero. As a
result, the substance conversion in the electrolyzer also returns
to the corresponding initial value as soon as the grid frequency
has stabilized again.
[0024] If the grid frequency stabilized in this manner deviates
from the nominal frequency of the AC voltage grid, primary
balancing power is automatically provided and the instantaneous
reserve power is no longer required. The electrolysis device
therefore provides instantaneous reserve power only for a
comparatively short period, with the result that the inertia of the
substance conversions in the electrolyzer, which makes it necessary
to start up pumps and fans, still does not play a role. The
additional or reduced conversion, which takes place during the
change in the grid frequency, can therefore be buffered in the
electrolyzer, for example by tolerating a brief positive pressure
or negative pressure in the electrolyzer and removing it again by
means of subsequent measures during operation of the electrolyzer
after the grid frequency has stabilized.
[0025] The disclosure is therefore based on the knowledge that a DC
load connected to a voltage-setting converter need not necessarily
be able to convert a change in the AC power drawn from the AC
voltage grid just as quickly into a change in the DC power used for
the intended purpose. Rather, it suffices if the DC load can at
least briefly process and possibly internally buffer the changed DC
power. In this case, an electrolyzer, in particular, proves to be a
particularly advantageous DC load since, on the one hand, an
electrolyzer can be immediately prompted to change the DC power,
for example by virtue of the converter changing the DC voltage at
the electrolyzer, and, on the other hand, said buffering inherently
takes place in an electrolyzer, with the result that the likewise
inherent inertia of the electrolyzer does not prevent an at least
brief change in the DC power.
[0026] The voltage-impressing behavior of the electrolysis device
can therefore be achieved according to the disclosure even though
neither a resistive consumer nor an energy source or an energy
store is connected to the converter.
[0027] During voltage-impressing operation of the converter, the
converter can provide an instantaneous reserve power. For this
purpose, it is possible to use a control structure which emulates
the behavior of a synchronous machine with respect to frequency
changes. This behavior stabilizes the grid frequency in a
comparable manner to conventional power plants. Alternatively, it
is possible to use droop mode control which was mentioned at the
outset and comprises a frequency/power characteristic curve. Such
control is likewise able to stabilize the grid frequency and may
additionally comprise a voltage/reactive power characteristic curve
which can be used to also stabilize the grid voltage in addition to
the grid frequency and possibly to set up or stabilize an island
grid in which further energy generation units can also be
incorporated.
[0028] The change in the AC active power drawn from the AC voltage
grid results in a change in the DC voltage at the electrolyzer,
wherein the change in the DC voltage at the electrolyzer results in
a change in a DC power consumed by the electrolyzer, which change
corresponds to the change in the AC active power. As a result, the
change in the AC active power drawn from the AC voltage grid can be
immediately passed on to the electrolyzer as a change in the DC
power consumed by the electrolyzer.
[0029] In one embodiment of the method, a voltage transformation
can be produced between the electrolyzer and the converter by means
of a first DC/DC converter. As a result, the adjustment range of
the DC voltage at the electrolyzer can be extended in comparison
with the voltage range which can be adjusted by the converter on
the DC voltage side, such that the power consumption of the
electrolyzer can also be adjusted over a wider range.
[0030] In addition, the converter can exchange electrical power
with a PV generator connected on the DC voltage side, wherein the
PV generator is connected to a DC link circuit in parallel with the
electrolyzer. In this case, an electrical power generated by the PV
generator is fed either into the electrolyzer or into the AC
voltage grid. As a result, the electrolyzer can be supplied in a
cost-effective manner with regeneratively generated electrical
power which would otherwise have to be obtained from the AC voltage
grid.
[0031] In a further embodiment of the method, the converter can
exchange electrical power with a battery connected on the DC
voltage side, wherein the battery is connected to the DC link
circuit in parallel with the electrolyzer via a second DC/DC
converter. The battery makes it possible to buffer electrical power
and can decouple the power obtained from the grid from the
electrolyzer power in terms of time.
[0032] In the embodiments of the method in which a DC/DC converter
is arranged between the converter and a unit on the DC voltage
side, the DC/DC converter can be used to stabilize the voltage of
the DC link circuit. Specifically, controlling of the DC/DC
converter may comprise feedforward control, wherein the feedforward
control is used to set a DC current setpoint of the DC/DC converter
on the basis of a phase difference between the grid voltage and the
AC voltage at the input of the converter. The phase difference may
be processed further by a d-q coordinate system and is proportional
to the power drawn from the grid. As a result, the DC/DC converter
is prompted to already change its power in the event of a change in
the phase difference and not only in response to a change in the
voltage in the DC link circuit
[0033] The feedforward control is used to immediately modify the DC
current setpoint of the DC/DC converter on the basis of a change in
the grid frequency. As a result, a change in the voltage at the DC
link circuit, which occurs on account of a change in the AC active
power in response to the change in the grid frequency, is
anticipated as it were. The controlling of the DC/DC converter is
therefore such that the DC/DC converter immediately stabilizes the
DC link circuit in the event of changes in the grid frequency. In
the case of fast changes in the grid frequency, that is to say in
the case of high rates of change of the grid frequency, which cause
accordingly large phase differences and therefore particularly
large changes in the AC power, the DC/DC converter must quickly
additionally deliver or remove energy in order to prevent the DC
link voltage from dropping or increasing excessively. For this
purpose, the DC current setpoint for the DC/DC converter is
subjected to feedforward control by means of the phase phi between
the grid voltage and the power converter voltage and the control
dynamic response is therefore increased.
[0034] The voltage at the DC link circuit can be stabilized by the
first DC/DC converter and the electrolyzer connected to the latter
and/or possibly by the second DC/DC converter and the battery
connected to the latter. In this case, the phase difference may act
on the clocking of the DC/DC converters directly or via a
corresponding filter.
[0035] An electrolysis device according to the disclosure having an
electrolyzer which is connected to a converter and draws electrical
AC active power from an AC voltage grid via the converter is
characterized in that the converter is configured to be operated in
a voltage-impressing manner, such that a change in the grid
frequency in the AC voltage grid causes an immediate change in the
AC active power drawn from the AC voltage grid. This disclosure is
based on the knowledge that the immediate responses of the
converter to changes in the grid frequency, associated with
voltage-impressing operation, in the form of changes in the AC
active power drawn from the AC voltage grid can be immediately
passed on to an electrolyzer. Although the electrolyzer itself is
not able to permanently make a correspondingly fast change in the
converted power, it can be immediately prompted, on the one hand,
to change the DC power, for example by virtue of the converter
changing the DC voltage at the electrolyzer, and, on the other
hand, can buffer a brief deviation between a power impressed from
the outside and a DC power setpoint which is static per se.
[0036] In one embodiment, the electrolysis device may comprise a
first DC/DC converter which is arranged between the electrolyzer
and the converter. As a result, the adjustment range of the voltage
at the electrolyzer can be extended in comparison with the voltage
range which can be adjusted by the converter on the DC voltage
side, such that the power consumption of the electrolyzer can also
be adjusted over a wider range.
[0037] In a further embodiment, the electrolysis device may
comprise a photovoltaic generator which is connected to a DC link
circuit of the electrolysis device in parallel with the
electrolyzer on the DC voltage side. The photovoltaic generator can
be used to favorably supply the electrolyzer with regeneratively
generated electrical power which would otherwise have to be
obtained from the AC voltage grid.
[0038] In a further embodiment, the electrolysis device may
comprise a battery which is connected to the DC link circuit of the
electrolysis device in parallel with the electrolyzer via a second
DC/DC converter on the DC voltage side. The battery makes it
possible to buffer electrical power and can decouple the power
obtained from the grid from the electrolyzer power in terms of
time.
[0039] In a method for providing instantaneous reserve power for an
AC voltage grid by means of a converter which draws electrical AC
power from the AC voltage grid and supplies an electrolyzer with
electrical DC power, the converter is operated in a
voltage-impressing manner, such that a change in the grid frequency
in the AC voltage grid causes an immediate change in the AC active
power drawn from the AC voltage grid. In this case, an electrolyzer
proves to be an advantageous DC load for the voltage-impressing
converter since an electrolyzer, on the one hand, can be
immediately prompted to change the DC power, for example by virtue
of the converter changing the DC voltage at the electrolyzer, and,
on the other hand, electrical energy is buffered in the
electrolyzer, with the result that the electrolyzer, despite its
inherent inertia, tolerates well a brief change in the DC power and
therefore well supports brief changes in the AC active power for
supporting the grid frequency as part of the instantaneous
control.
[0040] During normal operation within the scope of the method
according to the disclosure, that is to say, in particular, in the
case of a grid frequency corresponding to a nominal frequency of
the AC voltage grid, the power drawn from the AC voltage grid and
supplied to the electrolyzer may be between 50% and 100% of a
nominal power of the electrolyzer. In this case, the electrolyzer
has a maximum power which is above the nominal power, wherein the
nominal power can correspond, in particular, to an operating point
which is distinguished by maximum efficiency of the electrolyzer.
Owing to the principle involved, the electrolyzer can therefore
consume a DC power which is above the nominal power, in particular
if the electrolyzer is operated only briefly at this operating
point.
[0041] In one embodiment of the method, the converter can exchange
electrical power with a battery connected on the DC voltage side if
a change in the grid frequency causes a change in the AC power and
the DC power supplied to the electrolyzer is outside an operating
range of the electrolyzer. In this case, the operating range can be
limited by a lower onset power of between 10% and 20% of the
nominal power and an upper maximum power of between 110% and 120%
of the nominal power of the electrolyzer. The battery may be
connected to a DC link circuit of the converter in parallel with
the electrolyzer via a DC/DC converter.
[0042] In a further embodiment of the method, the converter can
exchange electrical power with a photovoltaic generator connected
on the DC voltage side. During normal operation, that is to say, in
particular, in the case of a grid frequency which corresponds to a
nominal frequency of the AC voltage grid, the PV generator can be
operated at a maximum power point and the electrolyzer can be
operated with nominal power. The power of the PV generator is
reduced if a change in the grid frequency occurs which causes the
converter to reduce an AC power currently being fed in or to
increase an AC power currently being drawn. However, if a change in
the grid frequency occurs which causes the converter to increase an
AC power currently being fed in or to reduce an AC power currently
being drawn, the DC power of the electrolyzer is reduced. As a
result, instantaneous reserve is available at any time in both
directions.
BRIEF DESCRIPTION OF THE FIGURES
[0043] The disclosure is described and explained further below on
the basis of example embodiments illustrated in the figures.
[0044] FIG. 1 shows an electrolysis device according to the
disclosure having a converter and an electrolyzer;
[0045] FIG. 2 shows a device having a converter and a plurality of
DC loads;
[0046] FIG. 3 shows a further electrolysis device having a
converter, a DC/DC converter and an electrolyzer;
[0047] FIG. 4 shows an electrolysis device according to FIG. 3 with
a control device;
[0048] FIG. 5 shows an electrolysis device according to FIG. 3 or 4
with a PV generator;
[0049] FIG. 6 shows a method for operating a device according to
FIG. 3, 4 or 5;
[0050] FIG. 7 schematically shows the electrical powers in a device
which is operated using a method according to FIG. 6;
[0051] FIG. 8 shows a further electrolysis device having a
converter, an electrolyzer, a DC/DC converter and an energy store;
and
[0052] FIG. 9 shows an electrolysis device according to FIG. 8
having a further DC/DC converter and a PV generator.
DETAILED DESCRIPTION
[0053] FIG. 1 shows an electrolysis device 10 having an
electrolyzer 11 and a converter 12. The converter 12 is connected
to an AC voltage grid 15 via an input 12a on the AC voltage side, a
decoupling inductance 13, for example, an inductor, and a grid
connection point 14 and draws electrical power from the AC voltage
grid 15. The electrolyzer 11 is connected to a DC-voltage-side
output 12b of the converter 12 and is supplied with electrical
power by the converter 12.
[0054] The converter 12 may have a DC link circuit and, in one
embodiment, has a three-phase design, such that the converter 12
can be connected to a three-phase AC voltage grid 15 in order to
draw electrical AC power from the AC voltage grid 15 in three
phases. The converter 12 may be, in one embodiment, in the form of
a self-commutated transistor converter, wherein the transistors of
such a converter 12 may be composed of IGBTs and/or MOSFETs.
[0055] The electrolyzer 11 essentially constitutes a DC load and is
supplied with DC power by the converter 12. The DC power consumed
by the electrolyzer 11 depends in this case, via a current/voltage
characteristic curve, on the voltage which is applied to the
electrolyzer 11 and here corresponds to the voltage at the output
12b of the converter 12. Depending on the type and design of the
electrolyzer 11, the current/voltage characteristic curve may have
different onset voltages and gradients, in which case there is
generally a monotonous relationship between the current and the
voltage in a permissible input voltage range of the electrolyzer
11, with the result that the DC power consumed by the electrolyzer
11 is higher, the higher the applied voltage.
[0056] The electrolyzer 11 has a nominal power at which the
electrolyzer 11 can be operated with optimum efficiency. The
nominal power is composed of a nominal voltage in the permissible
input voltage range of the electrolyzer 11 and an associated
nominal current. In principle, input voltages above the nominal
voltage are also permissible and result in a higher power
consumption, wherein the overall efficiency of the electrolyzer 11
falls above the nominal power, for example on account of the
increased power requirement for auxiliary units such as pumps and
the like.
[0057] The converter 12 supplies the electrolyzer 11 with a DC
power which can be adjusted by the converter 12 on the basis of the
change in the current grid frequency of the AC voltage grid 15, in
particular by adjusting the voltage at the output 12b of the
converter 12 and therefore the input voltage of the electrolyzer 11
by means of the converter 12 on the basis of the change in the
current grid frequency of the AC voltage grid 15.
[0058] If the current grid frequency corresponds to the nominal
frequency and is constant, the converter 12 is operated in such a
manner that the electrolyzer 11 is supplied with a DC power which
is equal to or less than the nominal power of the electrolyzer 11.
In the case of a constant grid frequency, the DC power can, for
example, be set to a value of between 50% and 100% of the nominal
power of the electrolyzer.
[0059] The converter 12 has semiconductor switches which are not
illustrated in any more detail, are arranged in a bridge circuit
and are controlled by a control unit (not illustrated) in such a
manner that a flow of electrical power from the AC voltage grid 15
to the electrolyzer 11 via the converter 12 is established. In this
case, an AC voltage at the grid-side input 12a of the converter 12
can be controlled by means of suitable clocking of the
semiconductor switches in such a manner that a phase difference
between the grid voltage in the AC voltage grid 15 and the AC
voltage at the input 12a of the converter 12 is formed across the
decoupling inductance 13.
[0060] Such control can be used to set a desired electrical AC
active power by predefining a setpoint for the phase difference.
The desired electrical AC active power results from a setpoint of
the electrical DC power to be output by the converter 12 on the DC
voltage side and to be supplied to the electrolyzer. This DC
current setpoint is transformed in the control unit of the
converter 12 into the corresponding setpoint for the phase
difference between the grid voltage and the input-side AC voltage
at the converter 12, such that the setpoint for the phase angle is
a function of the desired DC load current. In this case, the
electrical AC active power which is drawn from the AC voltage grid
15 by the converter 12 is approximately proportional to the phase
difference which is established if the phase difference is small
with respect to Tr.
[0061] On the other hand, the phase difference between the grid
voltage and the AC voltage at the input 12a of the converter 12 is
controlled to the setpoint by the converter 12 itself, wherein the
actually flowing AC active power depends on which phase difference
is actually present. As a result, a change in the grid frequency,
which inevitably causes a change in the phase difference,
immediately results in a largely proportional change in the
electrical AC active power drawn from the AC voltage grid 15.
[0062] A frequency change in the AC voltage grid 15 therefore
correlates with a change in the phase angle, with the result that
the AC active power which is drawn likewise immediately changes in
the event of a change in the grid frequency. In this respect, the
converter 12 behaves in a voltage-impressing manner by virtue of
the AC active power drawn from the AC voltage grid 15 being
immediately reduced if the frequency falls and being immediately
increased if the frequency increases.
[0063] FIG. 2 shows a device 20 having a plurality of DC loads 21,
22, 23 and a converter 12. The converter 12 is connected to an AC
voltage grid 15 on the input side via a grid connection point 14
and draws electrical power from the AC voltage grid 15. The DC
loads 21, 22, 23 are connected to the DC link circuit 16 via one of
the switches 21a, 22a, 23a in each case and are supplied with
electrical power by the converter 12.
[0064] Both electrolyzers 11 and resistive loads, in particular
heating resistors or other resistors which are used, for example,
for surface finishing or metal processing, can be used here as DC
loads 21, 22, 23.
[0065] The DC loads 21, 22, 23 can each be connected to the
converter 12 or disconnected from the converter 12 via the switches
21a, 22a, 23a. As a result, the DC power flowing overall can be
adapted for a given voltage at the DC link circuit 16 of the
converter 12 by supplying electrical power to only a portion of the
DC loads 21, 22, 23, wherein the portion of the loads 21, 22, 23 to
be specifically supplied is selected by suitably controlling the
switches 21a, 22a, 23a.
[0066] FIG. 3 shows an electrolysis device 10 having an
electrolyzer 11 and a converter 12 according to FIG. 1, wherein a
DC/DC converter 32 is additionally arranged between the
electrolyzer 11 and the converter 12 and enables a voltage
transformation between the voltage at the DC-voltage-side output
12b of the converter 12 or at the DC link circuit 16 and the
voltage at the electrolyzer 11. The DC/DC converter 32 may be in
the form of a boost converter, a buck converter or a boost/buck
converter and/or may be configured for a bidirectional power flow,
for example.
[0067] Such DC/DC converters 32 are known to a person skilled in
the art in various embodiments which predominantly comprise clocked
semiconductor switches for setting the voltage transformation. In
particular, the DC/DC converter 32 may be in the form of a buck
converter for a unidirectional power flow from the converter 12 to
the electrolyzer 11, which converts the voltage of the DC link
circuit 16 into a relatively lower voltage at the electrolyzer 11,
wherein the transformation ratio can be set by means of a duty
factor, for example.
[0068] FIG. 4 shows details of a control system of the converter
12. A control device or circuit 41 generates control signals for
the converter 12 and for the DC/DC converter 32, which control
signals predefine, in particular, the control of the semiconductor
switches of the converter 12 and of the DC/DC converter 32. The
control signals may be predefined by the control device 41 on the
basis of a setpoint for an electrical DC power, wherein an actual
value of the DC power can be determined, for example, on the basis
of a current and voltage measurement which may be arranged, in
particular, between the DC/DC converter 32 and the electrolyzer 11.
The control device 41 determines a suitable duty factor, with which
the DC/DC converter 32 must be operated in order to set a suitable
voltage at the electrolyzer 11, with the result that the
electrolyzer 11 consumes the desired DC power. Since the voltage of
the DC link circuit 16 is at least as high as the rectified grid
voltage of the AC voltage grid 15, the DC/DC converter 32 makes it
possible to apply a considerably lower voltage than the rectified
grid voltage to the electrolyzer 11, in contrast to the embodiment
according to FIG. 1.
[0069] Assuming a given duty factor, the voltages on the two sides
of the DC/DC converter 32 are proportional to one another.
Therefore, a change in the voltage of the DC link circuit 16
results in a proportional change in the voltage at the electrolyzer
11 provided that the duty factor is not adjusted. Conventional
control systems are able to adjust the duty factor with a certain
delay, in which case various superordinate control aims can be
pursued. In particular, the voltage at the electrolyzer 11 and
therefore the DC power can be kept constant. Alternatively, the
voltage of the DC link circuit 16 can be kept constant.
[0070] As explained in connection with FIG. 1, the converter 12 can
operate in a voltage-impressing manner by immediately reducing the
AC active power which is drawn from the AC voltage grid 15, in
particular on the basis of the phase angle between the grid voltage
and the AC voltage at the input 12a of the converter 12, in the
event of a frequency reduction and immediately increasing the AC
active power in the event of a frequency increase. Such an
immediate change in the AC active power results in a corresponding
change in the voltage of the DC link circuit 16 provided that the
DC power remains unchanged. However, even a constant DC power does
not suffice to counteract a change in the voltage of the DC link
circuit 16 on account of a frequency-related change in the AC
active power. Therefore, the DC power must be adapted to the AC
power, in which case adjustment of the setpoint for the DC power on
the basis of the voltage of the DC link circuit 16 for the purpose
of stabilizing precisely this voltage constitutes an indirect and
accordingly delayed response.
[0071] The control device 41 therefore determines the instantaneous
phase difference between the grid voltage in the AC voltage grid 15
and the AC voltage at the input 12a of the converter 12 from
time-resolved measurements of the voltages upstream and downstream
of the decoupling inductance 13. This phase difference can be used
in the control device 41 for feedforward control of the setpoint of
the DC/DC converter 32. As a result, the setpoint for the DC power,
and therefore the duty factor of the DC/DC converter 32, is already
adapted in response to a change in the phase difference. This
adaptation already takes place before a significant change in the
voltage of the DC link circuit 16, which is associated with a
change in the AC active power, in particular if the AC active power
is changed on account of the voltage-impressing control of the
converter 12 in response to a change in the phase difference. This
considerably increases the dynamic response of the entire control
section.
[0072] FIG. 5 shows an electrolysis device 10 having a PV generator
51 which is connected to the DC link circuit 16 of the converter 12
in parallel with the electrolyzer 11. The electrical power of the
PV generator 51 can be adjusted via the voltage of the DC link
circuit 16 and can be either fed into the electrolyzer 11 or
exchanged with the AC voltage grid 15 via the converter 12. In this
case, the operating point of the PV generator 51 is set on the
basis of the voltage at the DC link circuit 16, whereas the voltage
at the electrolyzer 11 can be set independently via the DC/DC
converter 32.
[0073] FIG. 6 schematically shows an example sequence of a method
for providing balancing power by means of an electrolysis device 10
according to FIG. 5. During normal operation of the electrolysis
device 10, for example in the case of a balanced power balance in
the AC voltage grid 15 at a grid frequency which corresponds to the
nominal frequency of the AC voltage grid 15 and is largely constant
(act S1 in FIG. 5), the PV generator 51 can be operated at a
maximum possible power point P_MPP and the electrolyzer can be
operated with its nominal power P_Nenn (act S2).
[0074] In the event of a change in the grid frequency, the
converter 12 of the electrolysis device 10 responds with a change
in the AC active power (act S3). After S3, depending on the sign of
the power imbalance which results in a change in the grid
frequency, the method branches to acts S4a and S5a in the event of
a power deficit in the AC voltage grid 15 and to steps S4b and S5b
in the event of a power excess in the AC voltage grid 15.
[0075] At S5a, the change in the AC power counteracting the power
deficit in the AC voltage grid 15 is implemented in the
electrolysis device 10 by reducing the DC power P_Last of the
electrolyzer 11 in comparison with the nominal power P_Nenn. The PV
power P_PV of the PV generator 51 can remain unchanged at
P_MPP.
[0076] At S5b, the change in the AC power counteracting the power
excess in the AC voltage grid 15 in the electrolysis device 10 has
the opposite sign and could be implemented by increasing the DC
power P_Last of the electrolyzer 11 in comparison with the nominal
power P_Nenn. However, this proves to be disadvantageous, in
particular, when the maximum power is only slightly above the
nominal power of the electrolyzer 11 and/or the efficiency of the
electrolyzer 11 falls considerably at DC powers above its nominal
power. Therefore, additionally or alternatively at S5b, the PV
power P_PV is reduced in comparison with the maximum possible power
P_MPP. This is moreover possible at any time, in particular even at
night, when the maximum possible power P_MPP is equal to zero, by
feeding DC power back into the PV generator 51.
[0077] The DC powers P_Last and P_PV can be adjusted separately
from one another, in particular, in an electrolysis device 10
according to FIG. 5 or FIG. 9. The PV power P_PV is adjusted via
the voltage at the DC link circuit 16, whereas the DC power P_Last
of the electrolyzer 11 results from the voltage at the DC link
circuit 16 and the adjustable transformation ratio of the DC/DC
converter 32. By operating the electrolysis device 10 using the
method according to FIG. 6, it is therefore possible to provide
instantaneous reserve power for stabilizing the AC voltage grid 15,
in which case balancing power for eliminating a power deficit by
reducing the DC power of the electrolyzer 11 and balancing power
for eliminating a power excess by restricting the PV generator 51
are achieved.
[0078] FIG. 7 schematically shows an example division of the
provision of the balancing power on the basis of the power balance
in the AC voltage grid 15.
[0079] In the case of a balanced power balance, which can be
expressed, in particular, by the fact that the grid frequency is
constant and corresponds, in particular, to the nominal frequency
of the AC voltage grid 15, the PV generator 51 is operated with
maximum possible power P_MPP and the electrolyzer 11 is operated
with nominal power P_Nenn. The nominal power P_Nenn of the
electrolyzer 11 is a device property and can therefore be assumed
to be largely constant. A current sum of the powers P_PV and
P_Last, and therefore also the AC power exchanged with the AC
voltage grid 15 via the converter 12, therefore depends
substantially on the current solar radiation on the PV generator
51. During normal operation, depending on environmental conditions,
the AC power can therefore be between the nominal power P_Nenn of
the electrolyzer 11 (for example at night, without solar radiation)
and the difference between the nominal power P_Nenn of the
electrolyzer 11 and a nominal power of the PV generator 51. In a
possible special case in which the nominal powers of the
electrolyzer 11 and of the PV generator 51 are identical, the AC
power during normal operation is therefore between P_Nenn and
zero.
[0080] In the event of a power deficit in the AC voltage grid 15,
the DC power P_Last supplied to the electrolyzer 11 is reduced,
whereas the PV power P_PV can still correspond to the maximum
possible PV power P_MPP. A rate of change of the grid frequency can
be used, in particular, as a measure of the power deficit, such
that the power change is proportional to the rate of change of the
grid frequency, for example; this may similarly apply to a power
excess.
[0081] In the event of a power excess in the AC voltage grid 15,
the electrolyzer 11 is still operated with its nominal power
P_Nenn. In principle, the electrolyzer 11 could also be operated
with a power greater than P_Nenn, but generally only with reduced
efficiency and/or only briefly. In order to counteract the power
excess in the AC voltage grid 15, the power P_PV drawn from the PV
generator 51 is therefore additionally or alternatively reduced. In
this case, the PV power P_PV may become equal to zero and may
become negative, that is to say DC power may be fed back into the
PV generator 51 and consumed there. Since the maximum possible PV
power P_MPP can be occasionally very low, as described, for example
at night, the PV power P_PV can also be reduced solely by
increasing the power fed into the PV generator 51 on the basis of
the power excess in the AC voltage grid 15.
[0082] In a special configuration, the nominal power P_Nenn of the
electrolyzer 11 may correspond approximately to the nominal power
P_Peak of the PV generator 51. In this case, the complete nominal
power P_Nenn of the electrolyzer 11 is available for responding to
a power deficit in the AC voltage grid 15, whereas at least the
complete nominal power P_Peak of the PV generator 51 is available
at any time, in particular even at night, for responding to a power
excess in the AC voltage grid 15. Overall, an optimum symmetrical
balancing power band with positive and negative balancing power of
an identical order of magnitude is therefore provided by an
electrolysis device 10 configured in this manner.
[0083] In principle, many further configurations of the
electrolysis device 10 are conceivable, for example intermediate
variants with an electrolyzer 11 as a main component, which is
operated at approximately 50% of the nominal power P_Nenn during
normal operation, and with a PV generator 51 with a relatively low
nominal power P_PV<P_Nenn. In this case, the PV generator 51
carries out part of the power change in response to a power excess
in the AC voltage grid 15. The greater the nominal power P_Peak of
the PV generator, the higher the desired power P_Last of the
electrolyzer 11 during normal operation can also be selected to
be.
[0084] Another intermediate variant comprises an electrolysis
device 10 having a PV generator 51 as a main component, which is
operated with maximum possible power P_MPP during normal operation,
and having an electrolyzer 11 with a relatively low nominal power
P_Nenn<P_Peak. In this case, the electrolyzer 11 carries out the
power change in response to a power deficit in the AC voltage grid
15, with the result that it is possible to offer a symmetrical
balancing power band which is composed of the nominal power P_Nenn
of the electrolyzer 11, on the one hand, and, if necessary, equal
restriction of the PV generator 51, on the other hand, and
therefore only depends on the nominal power P_Nenn or makes this
fully usable for the instantaneous reserve.
[0085] FIG. 8 shows a further embodiment of an electrolysis device
10 having a converter 12 and an electrolyzer 11. In comparison with
FIG. 1, the electrolysis device 10 according to FIG. 8 additionally
comprises a battery 81 which is connected to the DC link circuit 16
of the converter 12 in parallel with the electrolyzer 11 via a
DC/DC converter 82. The DC/DC converter 82 can control, in
particular, the exchange of power between the DC link circuit 16
and the battery 81 in such a manner that the voltage at the DC link
circuit 16 is stabilized, in which case feedforward control similar
to FIG. 4 can be used, if appropriate. In addition, as a result of
the battery 81, there is a further degree of freedom available for
the specific configuration of the electrolysis device 10 according
to FIG. 8 in order to add exclusivity to individual contributions
to providing a symmetrical balancing power band as instantaneous
reserve. For example, a power change in response to a power deficit
in the AC voltage grid 15 can be implemented completely by reducing
the DC power P_Last of the electrolyzer 11 to a value below its
nominal power P_Nenn, whereas a power change in response to a power
excess in the AC voltage grid 15 is implemented completely by
feeding DC power into the battery 81; the energy thereby stored in
the battery can in turn be used to operate the electrolyzer 11.
[0086] FIG. 9 shows a further embodiment of an electrolysis device
10 having a converter 12 and an electrolyzer 11 connected to the
converter 12 via a DC/DC converter 32. In comparison with FIG. 3,
the electrolysis device 10 according to FIG. 9 additionally
comprises a battery 81 which, in a similar manner to FIG. 8, is
connected to the DC link circuit 16 of the converter 12 via a
further DC/DC converter 82, and a PV generator 51 which, in a
similar manner to FIG. 5, is likewise connected to the DC link
circuit 16 of the converter 12, possibly via a third DC/DC
converter which is not illustrated here. The electrolysis device 10
according to FIG. 9 therefore combines substantially the features
of the electrolysis devices 10 according to FIG. 5 and FIG. 8 and
therefore also has their advantages.
* * * * *